The present invention relates to a method and an apparatus for aligning the elevation of an automotive radar unit.
Radar is used in various automotive applications, for example as part of a forwards directed collision warning system, or adaptive cruise control system. Usually, a radar transceiver unit that transmits and receives radar waves is mounted in a forwards location on the vehicle behind a bumper or body panel which is substantially transparent to the radar waves. In such systems, the radar beam may be fixed or laterally scanning, single-beam or multiple-beam, but is directed forwards above the road surface towards other vehicles or obstacles on or at the side of a roadway. It is important for the radar beam to be aligned with the correct elevation, or else the beam will be directed downwards at the road surface or upwards where it may intercept bridges or other structures above the road.
An initial elevation alignment is usually done in the factory after the vehicle has been assembled. One way of aligning the elevation is with an electronic spirit level on a reference surface such as a housing of a radar transmitter unit. The elevation needs to be aligned to an accuracy of about xc2x10.75xc2x0. Such manual alignment is time consuming and prone to human error.
It may also be necessary to align the radar beam in the horizontal direction, usually with respect to a longitudinal center line of the vehicle. When the radar beam is scanned symmetrically to either side of the center line. Usually the radar beam is projected forwards from a central portion of a molded plastic vehicle bumper, and scanned symmetrically to either side of the vehicle longitudinal axis. Azimuth alignment may be done electronically when the radar beam is scanned. For example, an azimuth offset corresponding to a known discrepancy between the middle of the scan and the vehicle longitudinal central axis may be applied to signals generated by the radar transceiver from detected returned radar waves. In many applications of automotive radar, this alignment must be performed to angle having an accuracy of less than or equal to xc2x10.1xc2x0 to xc2x10.2xc2x0. It is difficult to achieve this level of accuracy while at the same time making an elevation alignment of an automotive radar transceiver unit.
It is an object of the present invention to provide a more convenient device and method for aligning the elevation, and optionally also the azimuth alignment, of an automotive radar unit.
Accordingly, the invention provides a method of aligning a radar transceiver unit on a vehicle, using at least three radar reflectors, comprising the steps of:
a) positioning the radar reflectors in a pattern in which the reflectors are fixed relative to one another with the reflectors occupying three rows at different elevations and at least three different horizontal positions, so that the middle row is horizontally distinguishable from the neighboring rows;
b) directing a beam of radar waves from the radar transceiver generally towards the radar reflectors;
c) scanning the beam relative to the pattern so that the beam moves across the pattern at one elevation in a horizontal direction;
d) receiving at the radar transceiver radar waves reflected from one or more of the reflectors;
e) detecting the elevation of the middle row, including repeating if necessary steps c) and d) at different elevations;
f) setting the elevation of the beam of radar waves according to the detected elevation of the middle row.
Normally, the vehicle will be positioned on a horizontal reference surface, with the longitudinal axis of the vehicle directed at least approximately towards the radar reflector pattern.
The pattern may be fixed relative to the vehicle, with the beam of radar waves being scanned horizontally across the pattern of radar reflectors, which may be mounted on a support in a plane at right angles to the vehicle longitudinal axis.
If the vehicle is positioned with a longitudinal center line of the vehicle aligned azimuthally (i.e. horizontally), but not necessarily vertically, with a radar reflector in the middle row, then the method may comprise additionally the steps of:
g) scanning the beam of radar waves over the pattern so that the beam moves across said reflector in a horizontal direction;
h) receiving at the radar transceiver radar waves reflected from said reflector;
i) detecting the point in the scan at which the reflector is in alignment azimuthally with the beam of radar waves to set the azimuth alignment of the scanned beam.
For example, it may be known that the reflector returns a maximum signal when the beam of radar waves is centered on the reflector. Then the center of the reflector would be placed either on or directly above or below the longitudinal center line of the vehicle.
In one embodiment of the invention, the elevation separation between the middle row and neighboring rows is such that in step d) the radar transceiver does not detect reflected radar waves from reflectors in said neighboring rows when the elevation of the beam of radar waves is at the elevation of the middle row. Then when no corresponding signal is received from the neighboring rows, while a signal is received from the middle row, it Is known that the elevation of radar beam is such that the beam is directed onto the middle row. The elevation can then be fixed. An advantage of this approach is that the separation of the neighboring rows from the middle row can be set such that the range of elevation over which no signal is returned from the neighboring rows corresponds with an allowable tolerance in the set elevation of the radar transceiver.
In an alternative embodiment, the elevation separation between the middle row and neighboring rows is such that the radar transceiver detects with equal reduced strength reflected radar waves from reflectors in said neighboring rows when the elevation of radar waves is at the elevation of the middle row. This has the advantage that it may be possible to set the elevation more accurately, as for most radar beam profiles there will be only one elevation at which the signals from neighboring rows are matched.
In one embodiment of the invention, there are at least five radar reflectors, the number of and/or horizontal separation between radar reflectors in each row serving after steps c) and d) to identify uniquely each row. For example, the middle row may contain just one reflector, and each neighboring row may contain a pair of reflectors, but with the separation between reflectors in each pair of reflectors being different. Then, if the beam of radar waves is horizontally scanned repeatedly with respect to the radar reflector pattern at various elevations, with each scan being conducted at the same speed, then the difference in time between the detection of a pair of the reflectors can be used to identify which of the neighboring rows of reflectors has been detected.
Also according to the invention, there is provided an apparatus for aligning a radar transceiver unit on a motor vehicle, comprising a motor vehicle with a radar transceiver that generates a beam of radar waves, at least three radar reflectors for reflecting the beam back to the radar transceiver when a reflector is illuminated by the beam, and means for scanning the beam relative to the pattern at one elevation in a horizontal direction, wherein: the radar reflectors are arranged in a pattern in which the reflectors are fixed relative to one another with the reflectors occupying three rows at different elevations and at least three different horizontal positions such that the middle row is horizontally distinguishable from the neighboring rows, so that the elevation of the beam of radar waves may be set according to the detected elevation of the middle row.